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Keeping a lid on it: muscle scars and the mystery of the Mobergellidae

Topper, Timothy P.; Skovsted, Christian B.

Keeping a lid on it: muscle scars and the mystery of the Mobergellidae Thumbnail


Authors

Timothy P. Topper

Christian B. Skovsted



Abstract

Mobergellans were one of the first Cambrian skeletal groups to be recognized yet have long remained one of the most problematic in terms of biological function and affinity. Characterized by a disc-shaped, phosphatic sclerite, the most distinctive character of the group is a prominent set of internal scars, interpreted as representing sites of former muscle attachment. Predominantly based on muscle scar distribution, mobergellans have been compared to brachiopods, bivalves and monoplacophorans; however, a recurring theory that the sclerites acted as an operculum remains untested. Rather than correlate the number of muscle scars between taxa, here we focus on the percentage of the inner surface shell area that the scars constitute. We investigate two mobergellan species, Mobergella holsti and Discinella micans, and compare the Cambrian taxa with the muscle scars of a variety of extant and fossil marine invertebrate taxa to test whether the mobergellan muscle attachment area is compatible with an interpretation as operculum. The only skeletal elements in our study with a comparable muscle attachment percentage are gastropod opercula. Complemented with additional morphological information, our analysis supports the theory that mobergellan sclerites acted as an operculum presumably from a tube-living organism. The paucity of tubes co-occurring with mobergellan sclerites could be explained by the transportation and sorting of detached opercula, while the corresponding tube remained attached to substrata in shallower water. The operculum perhaps performed a similar role to that seen in serpulid annelids and in neritid gastropods sealing the living chamber of the organism to avoid desiccation or for protection.

Citation

Topper, T. P., & Skovsted, C. B. (2017). Keeping a lid on it: muscle scars and the mystery of the Mobergellidae. Zoological Journal of the Linnean Society, 180(4), 717-731. https://doi.org/10.1093/zoolinnean/zlw011

Journal Article Type Article
Acceptance Date Jan 25, 2017
Online Publication Date Jan 31, 2017
Publication Date Aug 1, 2017
Deposit Date May 16, 2017
Publicly Available Date Mar 29, 2024
Journal Zoological Journal of the Linnean Society
Print ISSN 0024-4082
Electronic ISSN 1096-3642
Publisher Linnean Society of London
Peer Reviewed Peer Reviewed
Volume 180
Issue 4
Pages 717-731
DOI https://doi.org/10.1093/zoolinnean/zlw011

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Copyright Statement
This is a pre-copyedited, author-produced PDF of an article accepted for publication in Zoological Journal of the Linnean Society following peer review. The version of record Topper, Timothy P. & Skovsted, Christian B. (2017). Keeping a lid on it: muscle scars and the mystery of the Mobergellidae. Zoological Journal of the Linnean Society 180(4): 717-731 is available online at: https://doi.org/10.1093/zoolinnean/zlw011.




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